A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a vehicle is equipped with a navigation function to guide a driver to a destination through a calculated route. Such a navigation system detects the position of the user's vehicle, and reads out map data pertaining to an area at the current vehicle position from a data storage medium, for example, a CD-ROM (compact disc read-only memory), a DVD (digital versatile disc), or a hard disc. Typically, the navigation system displays a map image on a monitor screen while superimposing thereon a mark representing the current location of the user. At an intersection, the navigation system notifies the user which direction to turn at the intersection.
When a destination is specified, the navigation system in the conventional technology creates a route to the destination based on map data stored therein and a navigation program and computer provided therein. In general, however, the computing power of a navigation system such as an automobile (vehicle) navigation system or portable navigation system is lower than that of a remote navigation server. This is because the computer in the vehicle navigation system or portable navigation system is designed for low cost and small size.
For an optimum performance of such a navigation system, it is required that the map data be updated frequently in order to reflect recent changes in the roads, new roads, development of new areas, etc. and to produce an accurate route. Moreover, for calculation of an optimum route to a selected destination, it is desirable that the processing speed of the navigation system be high enough. Thus, the navigation system must have a map database which is constantly updated and the high performance processor.
Because of such requirements, in the recent navigation systems, a remote navigation server with high computer power and updated map data is used for establishing a calculated route to the destination. The remote navigation server sends the required routing data to each user's navigation system. Thus, the user can make use of the calculated route created by the remote server based on the high computing power and the most recent map data.
In such a navigation system using the remote navigation server, it is desirable to minimize the amount of routing data sent from the remote navigation server to the individual navigation system.